This invention relates to a four-cycle crankcase compression engine and more particularly to an improved pressure-controlling and throttling arrangement for such engines as well as an improved EGR system for controlling nitrous oxide (NO.sub.x) emissions.
It has been proposed to form a four-cycle internal combustion engine in such a manner that the crankcase chamber serves as a compression chamber for compressing the charge that is delivered to the induction system. Several very effective embodiments for achieving this purpose are shown in my U.S. Pat. No. 5,377,634, issued Jan. 3, 1995 and entitled "Compressor System For Reciprocating Machine," which patent is assigned to the assignee hereof.
In that patent and in other instances, an arrangement has been incorporated for limiting the maximum boost pressure by bypassing a portion of the compressed charge back to the intake side upstream of the point of admission to the crankcase chamber. Although this arrangement has some advantages, it also has some disadvantages.
First, by passing the pressurized charge back to the induction system upstream of the crankcase chamber, the actual pressure in the induction system varies. This can give rise to problems on deceleration and may, in some instances, provide erratic operation. This is particularly true if the charge former is placed in the induction system. The varying pressure in the induction system can cause erratic performance of the charge former and/or even reverse flow of the gases to the atmosphere.
This problem in connection with the charge former can be avoided, of course, by locating the charge former on the downstream side. However, if this is done, there is still a problem in that the engine experiences high pumping losses. Also, the throttle arrangement utilized in that type of device does not permit as wide a control over engine running as may be desired.
It is, therefore, a principal object of this invention to provide an improved pressure control system for a four-cycle engine embodying crankcase compression.
It is a further object of this invention to provide an improved pressure control system for a crankcase compression four-cycle engine.
In conjunction with engine operation, there is increased emphasis on the controlling of the emission of gasses, particularly from the exhaust of the engine, that may have some undesirable effects. One of these gasses are oxides of nitrogen, referred to commonly as NO.sub.x. NO.sub.x results from high temperatures in the combustion chamber that cause oxides of nitrogen to form. One way of combating the formation of NO.sub.x is through the use of an exhaust gas recirculation (EGR) arrangement. That is, under some running conditions when nitrous oxides may be generated, the combustion temperature is lowered by recycling exhaust gasses into the combustion chamber.
Although this method of controlling NO.sub.x is effective, it has resulted in very complicated arrangements. That is, it is necessary to collect the exhaust gasses, generally in the exhaust system, and re-convey them to the cylinder. It is important that each cylinder receive the appropriate amount of exhaust gas recirculation. This obviously results in the use of considerable plumbing and control valves.
It is, therefore, a further principal object of this invention to provide an improved and simplified EGR system for engines.
It is a still further object of this invention to provide an EGR system for engines wherein the EGR system is basically internal and requires no valves or significant external conduits. In addition, the ideal system would serve each cylinder individually.
As will become apparent from the following description, this object is accomplished by providing an EGR accumulator device that communicates with each individual cylinder of the engine through a communication port in the cylinder bore. The communication port is positioned so that it is uncovered only when the piston is near its bottom dead center position. In this way, the exhaust gasses can accumulate in the accumulator chamber and be released during the intake stroke for internal exhaust gas recirculation.
One problem with such an arrangement is the positioning of the port for the exhaust gas accumulator chamber may be uncovered to the crankcase at times or may be disposed in a location so that lubricant can flow into proximity with the communication port. The port should, of course, be relatively small in size, and this gives rise to the possibility of deposits being formed and blocking the port from carbonization of the lubricant.
It is, therefore, a still further object of this invention to provide an internal EGR system for an engine wherein the porting and lubrication system is arranged in such a manner that the port will not easily become clogged.